Method and apparatus for manufacturing battery electrode plate and battery using the same

ABSTRACT

A battery electrode plate ( 19 ) is produced via an active material impregnation step for impregnating an entire porous core substrate shaped like a thin plate ( 1 ) with an active material ( 3 ), a pressing step for performing press working on the core substrate to form a plurality of rail shaped protrusions ( 8 ), an active material removal step for removing the active material to form core substrate exposed sections ( 13 ) by applying ultrasonic vibrations to the rail shaped protrusions, a flattening step for compressing the core substrate exposed sections down to an identical level with the other sections, and a cutting step for cutting predetermined sections including the core substrate exposed sections.

REFERENCE TO RELATED APPLICATION

[0001] This is a divisional application of Ser. No. 10/111,665, filedMay 22, 2002.

TECHNICAL FIELD

[0002] The present invention relates to a battery electrode plate usedin a rechargeable battery such as a nickel metal hydride battery or anickel cadmium battery, and more particularly to a method and apparatusfor manufacturing a non-sintered battery electrode plate including afoamed metal core substrate impregnated with an active material, and abattery using such a battery electrode plate.

BACKGROUND ART

[0003] Amongst electrode plates for rechargeable batteries, thoseproduced using a foamed metal with a three dimensional network structureas a core substrate, by impregnating the core substrate with an activematerial, display comparatively superior discharge capacities, and arewidely used. In addition, in recent years there has been strong demandfor improvements in the high rate discharge characteristics ofbatteries, and as a result, new battery electrode plate manufacturingmethods have been proposed, such as that shown in FIG. 7A to FIG. 7Edisclosed in Japanese Laid-Open Patent Publication No. 2000-77054.Firstly, in a first pressing process, two slots 2 of predetermined widthare formed in a core substrate 1 composed of a foamed metal, with thetwo slots parallel with both edges of the core substrate. Once the coresubstrate 1 has been impregnated with an active material 3, the activematerial 3 accumulated inside the slots 2 is removed using a brush orthe like. Subsequently, in a second pressing process, the core substrate1 is subjected to three press working steps and converted to a formshown in FIG. 7C in which the entire surface is level with the bottom ofthe slots 2. The sections where the slots 2 had been formed are thensubjected to an active material removal process using a brush and an airblower to form core substrate exposed sections 4 as shown in FIG. 7D.The core substrate 1 is then cut, forming battery electrode plates 7.

[0004] A current collector 7 b including the core substrate exposedsection 4 is formed on one edge of the battery electrode plate 7, and acylindrical electrode group formed by winding this electrode plate has acurrent collector on one end surface. Because this electrode groupcollects current uniformly along the entire length of the batteryelectrode plate, the current collecting efficiency improves. Inaddition, by employing a tab-less method wherein a current collectinglead plate is welded to the aforementioned current collector, thecurrent collection characteristics improve markedly, enabling thedemands for improvements in high rate discharge characteristics to bemet.

[0005] However, the battery electrode plate 7 prepared by the processesdescribed above suffers from the problems described below. A firstproblem is that because variations in the impregnation density of theactive material 3 occur within active material impregnated sections 7 a,there is a variation in the capacity of batteries produced using thesebattery electrode plates 7, and so when applied to a battery pack, thereis an increased likelihood of over charging or over discharging.

[0006] A second problem is that because a boundary line 7 c between theactive material impregnated section 7 a and the current collector 7 b isnot a true straight line, the precision of the dimensions and shape ofthe battery electrode plate 7 is low, leading to a reduction in thecurrent collecting function of a battery produced using this batteryelectrode plate 7, and a failure to achieve high rate dischargecharacteristics.

[0007] A third problem is that because the removal of the activematerial 3 from the current collector 7 b is imperfect, there is anincreased likelihood of unsatisfactory welding occurring duringattachment of the current collecting lead plate to the current collector7 b, resulting in a reduced yield. Removal of the active material usinga brush and air blower is also inefficient, and invites a reduction inproductivity.

[0008] A fourth problem is that the width of the core substrate exposedsections 4 shown in FIG. 7D, prior to cutting, differs from the presetvalue. As a result, a method wherein the core substrate exposed sectionis folded at right angles and then compressed to form the currentcollector cannot be applied, and so it becomes impossible to ensure themechanical strength of the current collector or a high currentcollection efficiency.

[0009] A fifth problem is that the battery electrode plates 7 obtainedby cutting the core substrate 1 are susceptible to warping into a bowshape. When the battery electrode plate 7 is wound into a spiral shapeto form an electrode group, this warping can be the cause of weaving,resulting in an electrode group of an unsatisfactory shape. Moreover,not only does this warping occur, but when viewed at magnification undera microscope, it is apparent that fine cracks also develop at theboundary section between the active material impregnated section 7 a andthe current collector 7 b, and sections of the metallic skeleton of thecore substrate 1 rupture, leading to a deterioration in strength. As aresult, this type of battery electrode plate 7 is susceptible toproblems such as dropout of the active material 3, short circuiting, anddeterioration in the electrical conductivity.

[0010] Japanese Laid-Open Patent Publication No. 2000-77054 disclosesanother method of manufacturing a battery electrode plate. This methodinvolves impregnating an entire core substrate composed of a foamedmetal with an active material, subsequently carrying out press workingto compress the entire core substrate to a predetermined thickness, andthen forming core substrate exposed sections by removing the activematerial from certain regions using an ultrasonic vibration device.

[0011] However in this method, because the boundary line between theactive material impregnated sections and the current collector of thebattery electrode plate is not a true straight line, there is adeterioration in the current collecting function of a battery producedusing this battery electrode plate, and high rate dischargecharacteristics are unobtainable. This is because a large amplitudeultrasonic vibration must be applied in order to remove the activematerial after the press working, and as a result, even the activematerial in the regions surrounding the core substrate exposed sectionsis removed. In addition, there is a danger that the metallic skeleton ofthe core substrate may suffer damage or deterioration when exposed tolarge amplitude ultrasonic vibrations.

[0012] Consequently, the present invention takes the conventionalproblems described above into consideration, with an object of providinga method and apparatus for manufacturing a battery electrode plate inwhich there is no variation in the impregnation density of the activematerial, the boundary line between the active material impregnatedsections and the current collector is a true straight line, the residualratio of the active material in the current collector is low, and theentire current collector has a predetermined width, as well as providinga battery which utilizes such a battery electrode plate.

DISCLOSURE OF THE INVENTION

[0013] In order to achieve the above object, a method for manufacturinga battery electrode plate according to the present invention includes anactive material impregnation step for impregnating an entire porous coresubstrate shaped like a thin plate with an active material; a pressingstep for performing press working on the active material impregnatedcore substrate to form a plurality of rail shaped protrusions; an activematerial removal step for removing the active material to form coresubstrate exposed sections by applying ultrasonic vibrations to the railshaped protrusions; a flattening step for pressing down on the top ofthe core substrate exposed sections and compressing the exposed sectionsdown to the same level as the other sections; and a cutting step forcutting predetermined sections including the core substrate exposedsections to form individual battery electrode plates.

[0014] An electrode group produced by spirally winding the batteryelectrode plates of a positive and negative electrode produced by theabove method, with a separator interposed therebetween, can be placedwithin a cylindrical battery case to form a cylindrical battery.

[0015] Another method for manufacturing a battery electrode plateaccording to the invention includes an active material impregnation stepfor impregnating an entire porous core substrate shaped like a thinplate with an active material; a pressing step for performing pressworking on the active material impregnated core substrate to form aplurality of rail shaped protrusions; an active material removal stepfor removing the active material to form core substrate exposed sectionsby applying ultrasonic vibrations to the rail shaped protrusions; a coresubstrate exposed section compression step for compressing the coresubstrate exposed sections; a lead welding step for seam welding a leadhoop to the core substrate exposed sections; and a cutting step forcutting predetermined sections including the lead hoop to formindividual battery electrode plates.

[0016] An electrode group produced by alternately laminating the batteryelectrode plates of a positive and negative electrode produced by theabove method, with a separator interposed therebetween, can be placedwithin a prismatic battery case to form a prismatic battery.

[0017] An apparatus for manufacturing a battery electrode plate of thepresent invention includes a stripe roller press device for performingpress working on an active material impregnated core substrate formedfrom a porous core substrate shaped like a thin plate, to form aplurality of rail shaped protrusions; and an active material removaldevice including an ultrasonic vibration device for bringing anultrasound generation horn into contact with the rail shaped protrusionsand applying ultrasonic vibrations and a vacuum suction devicepositioned in an opposing position below each ultrasonic vibrationdevice for suctioning the active material removed by the application ofultrasonic vibrations.

[0018] Another apparatus for manufacturing a battery electrode plate ofthe invention includes a stripe roller press device for performing pressworking on an active material impregnated core substrate formed from aporous core substrate shaped like a thin plate, to form a plurality ofrail shaped protrusions; an active material removal device including anultrasonic vibration device for bringing an ultrasound generation horninto contact with the rail shaped protrusions and applying ultrasonicvibrations and a vacuum suction device positioned in an opposingposition below each ultrasonic vibration device for suctioning theactive material removed by the application of ultrasonic vibrations; awelding device for seam welding a lead hoop to a core substrate exposedsections formed by the active material removal device; and a cutter forcutting predetermined sections including the lead hoop to formindividual battery electrode plates.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1A, FIG. 1B, FIG. 1C, FIG. 1D, FIG. 1E and FIG. 1F areperspective views showing the sequence of production steps in a methodfor manufacturing a battery electrode plate according to a firstembodiment of the present invention;

[0020]FIG. 2A is a front view showing a stripe roller press device usedin a pressing step of the above method, and FIG. 2B is an enlarged viewof the portion IIB of FIG. 2A;

[0021]FIG. 3A is a front view showing an active material removal deviceused in an active material removal step, and FIG. 3B is a right handside view of the removal device;

[0022]FIG. 4 is a partially cutaway perspective view showing acylindrical battery containing a battery electrode plate produced by theabove method;

[0023]FIG. 5A, FIG. 5B, FIG. 5C, FIG. 5D, FIG. 5E, FIG. 5F and FIG. 5Gare perspective views showing the sequence of production steps in amethod for manufacturing a battery electrode plate according to a secondembodiment of the invention;

[0024]FIG. 6 is a partially cutaway perspective view of a prismaticbattery containing a battery electrode plate produced by the abovemethod; and

[0025]FIG. 7A, FIG. 7B, FIG. 7C, FIG. 7D and FIG. 7E are perspectiveviews showing the sequence of production steps in a conventional methodfor manufacturing a battery electrode plate.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] As follows is a description of preferred embodiments of thepresent invention, with reference to the drawings. FIG. 1A through FIG.1F are perspective views showing the sequence of production steps in amethod for manufacturing a battery electrode plate according to a firstembodiment of the invention. First, an entire core substrate 1 formedfrom a rectangular sheet of foamed metal of a predetermined size, shownin FIG. 1A, is impregnated with an active material 3 as shown in FIG.1B. The active material 3 is impregnated into the totally flat coresubstrate 1 prior to press working, and so is impregnated with a uniformdensity throughout the entire core substrate 1, and moreover because thesurface of the core substrate 1 is not irregular, namely there are noelevation differences, the active material 3 is retained within thesubstrate without flowing, and consequently dries with the uniformimpregnation density maintained. In this embodiment, the core substrate1 is a foamed nickel metal with a three dimensional network structure,and is formed as a rectangular thin sheet with a thickness of 1.24 mm,for example. However, the manufacturing method of this embodiment shouldpreferably be applied to a continuous strip type core substrate, namelya hoop core substrate.

[0027] Next, as shown in FIG. 1C, the entire surface of the coresubstrate 1 with the exception of those sections which form coresubstrate exposed sections 13 in subsequent steps, is subjected to pressworking, and the thickness of the substrate is compressed toapproximately half, from the aforementioned 1.24 mm, down to 0.6 mm forexample. At this point, two parallel rail shaped protrusions 8, 8 with athickness of approximately 0.9 mm to 1.1 mm are formed. A stripe rollerpress device 9 such as that shown in FIG. 2A is used for this pressworking.

[0028]FIG. 2A is a front view of the stripe roller press device 9, andFIG. 2B is an enlarged view of the portion IIB of FIG. 2A. The striperoller press device 9 includes a supporting press roller 10 and aworking press roller 11, wherein the supporting press roller 10 issupported at a fixed position but is free to rotate, and the workingpress roller 11 is subjected to a predetermined pressure toward thepress roller 10. Accordingly, the working press roller 11 possesses arigidity capable of withstanding the applied pressure, and is providewith annular slots 12, 12 at two predetermined positions around thecircumference of the roller for forming the protrusions 8, 8. As can beseen in FIG. 2B, the opening rim sections of the two side walls 12 a, 12b of the annular slots 12 are curved surfaces with a radius of curvatureR of 0.3 mm to 0.6 mm, for example.

[0029] Furthermore, the two press rollers 10, 11 have comparativelylarge roller diameters of 550 mm for example, and in the pressing stepof this embodiment, the active material impregnated core substrate 1which passes between the two press rollers 10, 11 is worked from thestate shown in FIG. 1B to the state shown in FIG. 1C in a single pressworking step in which a comparatively large pressure of 300 ton, forexample, is applied. The pitch of the two rail shaped protrusions 8, 8thus formed is determined by the dimensions of the annular slots 12, andconforms precisely to the preset value.

[0030] Whereas a conventional method for manufacturing a batteryelectrode plate includes two pressing steps, in the manufacturing methodof this embodiment, only one pressing step is needed for forming the twoprotrusions 8, 8, and so elongation and deformation of the coresubstrate is suppressed, although the single pressing step must be ableto ensure the predetermined thickness and the predetermined impregnationdensity of the active material 3 described above. As a result,experimental results revealed that 3 ton of load was necessary per 1 cmwidth of electrode plate. In practice, in order to ensure a uniformwidth for the protrusion 8 along the entire substrate, the gap betweenthe two press rollers 10, 11 should preferably be widened and set at avalue of 0.3 mm for example, and in such a case, an applied pressure of10 ton/cm is required.

[0031] Furthermore, because a foamed metal formed from pure nickel,which displays excellent expansibility, is used for the core substrate1, during the pressing step, those portions with a high impregnationdensity of the active material 3 display a larger degree of elongation.This variation in elongation is suppressed by increasing the rollerdiameter of the press rollers 10, 11. For example, whereas a pressroller with a diameter of 400 mm used in the second pressing step of theconventional manufacturing method shown in FIG. 7C generates alengthwise elongation of between 3.3% and 3.5%, the press rollers 10, 11with a diameter of 550 mm used in the embodiment generate an elongationof between 1.7% and 1.9% with the same compression ratio. In otherwords, the larger the roller diameter, the smaller the elongation of thecore substrate 1 will be. The reason for this observation is that thelarger the diameter of the press rollers become, the closer the processwill be to flat press working. Consequently, if press rollers 10, 11 oflarge roller diameter are used, then differences in the elongation rateresulting from variations in the impregnation density of the activematerial 3 is suppressed.

[0032] Furthermore, in the second pressing step of the conventionalmanufacturing method, pressing is performed three times using arelatively small press roller with a diameter of 400 mm, and produces alengthwise elongation of as much as 6%. This elongation is the cause ofthe bow shaped warping which occurs when the core substrate 1 is dividedinto individual battery electrode plates 7. In contrast, in the pressingstep of the manufacturing method according to this embodiment, becauseonly a single press working process is performed using press rollers 10,11 with comparatively large diameters, the lengthwise elongation isrestricted to a value between 1.7% and 1.9% as described above, and whenthe core substrate 1 is divided into individual battery electrode plates19 in a subsequent step, almost no warping or cracking occurs.

[0033] Moreover, in the pressing step, because the opening rim sectionsof the two side walls 12 a, 12 b of the annular slots 12 formed in theworking press roller 11 are curved surfaces with a radius of curvature Rof 0.3 mm to 0.6 mm, the boundaries between the protrusions 8, 8 and thesurrounding regions is clearly defined, and moreover rupture ordeterioration of the metal skeleton of the core substrate 1 does notoccur during the press working. If the radius of curvature R of thecurved surfaces is set to a value greater than the range from 0.3 mm to0.6 mm, the active material 3 of the edge of the protrusions 8, 8 maydrop out and the boundaries between the protrusions 8, 8 and thesurrounding regions becomes indistinct, whereas if the radius ofcurvature R is smaller than the aforementioned range, there is a dangerof rupture or deterioration of the metal skeleton of the core substrate1, and a battery produced using such a battery electrode plate woulddisplay a reduced current collecting efficiency.

[0034] Subsequently, in an active material removal step shown in FIG.1D, the active material 3 impregnated within the two protrusions 8, 8 isremoved, forming two rail shaped core substrate exposed sections 13, 13.FIG. 3A and FIG. 3B show an active material removal device 14 used inthis step, wherein FIG. 3A is a front view and FIG. 3B is a right handside view. The active material removal device 14 includes a pair ofultrasonic vibration devices 17, 17 for stripping away and removingactive material 3 by bringing ultrasound generation horns 17 a, 17 ainto contact with the tops of the protrusions 8, 8 and applyingultrasonic vibrations, and a pair of vacuum suction devices 18, 18positioned in an opposing position below each of the ultrasonicvibration devices 17, 17 for suctioning active material 3 which has beenstripped away and removed.

[0035] The ultrasound generation horns 17 a have a sloped surface 17 b,with a downhill pitch in the direction of the movement of the coresubstrate 1, at the contact surface with the core substrate 1, and thissloped surface 17 b prevents damage to the core substrate 1.Furthermore, in order to reduce abrasion, the sloped surface 17 b, and aflat contact surface 17 c which is a continuation of the sloped surface17 b, are formed using sintered carbides, and the main body of theultrasound generation horn 17 a is formed from titanium.

[0036] According to this active material removal device 14, the coresubstrate 1 is moved in the direction of the arrow shown in FIG. 3B,with the tops of the protrusions 8, 8 held in contact with theultrasound generation horns 17 a of the pair of positionally fixedultrasonic vibration devices 17, 17. By applying ultrasonic vibrationsto each protrusion 8, the metal skeleton is squeezed and the activematerial 3 contained therein is stripped away and removed, while at thesame time, the vacuum suction device 18 suctions out and removes activematerial 3 impregnated within the protrusion 8 and the region below theprotrusion. As a result, the active material 3 contained within theprotrusion 8 and the region therebelow is almost entirely removed,yielding a high quality core substrate exposed section 13.

[0037] As follows is a description of the reasons the residual ratio ofactive material 3 within the core substrate exposed section 13 isextremely low. The active material 3 to be removed in the aforementionedactive material removal step is the active material impregnated withinthe protrusion 8, and because the protrusion 8 has not been subjected topress working, the active material 3 is extremely easy to remove.Consequently, even in the case of active material 3 which contains abinder, which has proved extremely difficult to remove usingconventional methods, by applying ultrasonic vibration to the substrateby bringing the ultrasound generation horn 17 a of the ultrasonicvibration device 17 into contact with the substrate while applyingsuction from below with the vacuum suction device 18, the activematerial 3 is removed easily and completely.

[0038] According to actual measurements, the active material residualratio of a core substrate exposed section 13 formed through theaforementioned active material removal step is from 1 to 4%. Incomparison, the active material residual ratio of a core substrateexposed section 4 formed in the conventional manufacturing method ismuch higher, at 10% or more, and furthermore lumps of active material 3still exist, and these lumps are the main cause of spark generationduring the welding of the current collecting lead plates. Accordingly,these lumps are removed by hand, which leads to a further reduction inproductivity. Evaluation of the active material residual ratiosdescribed above was conducted by immersion into an aqueous solution ofacetic acid, which dissolves only the active material 3 withoutdissolving the nickel of the core substrate 1, and subsequentcalculation of the weight of residual active material 3 within the coresubstrate exposed section 4 or 13 based on the rate of change in theweight of the dissolved active material 3.

[0039] In order to reduce the active material residual ratio of the coresubstrate exposed section 13, in the case in which the thickness B ofthe rail shaped protrusion 8 is approximately 1.1 mm, and the thicknessD of the core substrate 1 following press working is approximately 0.6mm, the active material removal device 14 should preferably be operatedwith a gap C between the lower surface of the core substrate 1 and thecontact surface 17 c of the ultrasound generation horn 17 a set to avalue from 0.7 mm to 0.8 mm. Because the thickness D of the coresubstrate 1 following press working shown in FIG. 1C is precisely 0.58mm, the aforementioned gap C could be set to a smaller value than therange from 0.7 mm to 0.8 mm, although setting the gap to such a smallvalue has no effect on the active material residual ratio. In contrast,if the aforementioned gap C is set to a value greater than the 0.7 mm to0.8 mm range, then the active material residual ratio increases.

[0040] In addition, in the active material removal device 14, the activematerial 3 within the protrusion 8 is in a state which is easilyremoved, the core substrate 1 is able to be moved rapidly andcontinuously across the positionally fixed ultrasonic vibration device17 while removal of the active material 3 takes place, and the activematerial 3 is suctioned away by the vacuum suction device 18 underneaththe protrusion 8, and as a result the active material 3 is removedefficiently, and the productivity improves markedly. According to actualmeasurements, because the active material 3 is in a state which iseasily removed, the core substrate 1 can be moved at a rapid rate ofapproximately 450 mm/sec. In this active material removal step, if themovement speed of the core substrate 1 is set to a value slower than 50mm/sec and the time taken in removing the active material 3 is extended,then not only does the productivity drop, but the core substrate 1 alsobegins to rupture and holes similar to worm holes begin to appear.

[0041] Furthermore, in the active material removal step, the ultrasonicvibration device 17 is set and operated so as to produce an amplitudewithin a range from 25 to 50 μm. If the amplitude is smaller than thisrange, the time required for removal of the active material 3 lengthens,whereas if the amplitude is larger than the aforementioned range, thenalthough the removal efficiency of the active material 3 improves, themetal skeleton of the core substrate 1 ruptures and the mechanicalstrength deteriorates, and consequently the current collecting functiondeteriorates, and furthermore the active material 3 from regions near tothe core substrate exposed sections 13 is also partially stripped away,meaning the linearity of the boundary line between the core substrateexposed section 13 and the other regions also deteriorates.

[0042] In the active material removal step of the embodiment, althoughthe application of ultrasonic vibrations is used for removing the activematerial 3, there is no deterioration in the strength of the coresubstrate 1. This effect was confirmed by evaluation results from atensile tester. In contrast, in cases in which the application ofultrasonic vibrations is used for removing the active material 3impregnated in a conventional core substrate 1, the strength of the coresubstrate 1 typically falls by 50 to 70%. The reason for thisobservation is that in the conventional manufacturing methods, a coresubstrate 1 impregnated with an active material 3 is subjected to pressworking prior to the application of ultrasonic vibrations to the regionsto become current collectors, and consequently the active material 3 isin a state which is extremely difficult to remove. In contrast, in thisembodiment, the active material 3 impregnated in the protrusions 8, 8,which have undergone almost no press working, is removed, and moreoverthe ultrasonic vibrations are applied only to the top of the protrudingprotrusions 8, 8 and have little effect on the other regions, andconsequently the core substrate 1 suffers no deterioration in strength.

[0043] Next, the aforementioned core substrate exposed sections 13 arelightly compressed using a different press roller (not shown in thedrawings) from that shown in FIG. 2A, to yield the state shown in FIG.1E, in which the core substrate exposed sections 13 are level with theother regions containing impregnated active material 3. Finally, bycutting along the three cutting lines shown by alternate long and shortdash lines in FIG. 1E, four battery electrode plates 19 shown in FIG. 1Fare obtained. Each of these battery electrode plates 19 are of the samestrip form, and have a boundary line 19 c along the length of theelectrode plate between an active material impregnated section 19 a anda current collector 19 b from which the active material 3 has beenremoved.

[0044] According to actual measurements using a microscope, thelinearity of the boundary line 19 c between the active materialimpregnated section 19 a and the current collector 19 b of a batteryelectrode plate 19 formed via the steps described above has a smallerror of no more than 0.2 mm, whereas a battery electrode plate 7produced by a conventional method displays an error of up to 0.8 mm. Thereason for this observation is that whereas a conventional manufacturingmethod has a pressing step following the impregnation of the activematerial 3 in which three pressing operations are performed in order toachieve a predetermined impregnation density, in the manufacturingmethod of this embodiment, only a single press working step, for formingthe protrusions 8, 8 shown in FIG. 1C on the core substrate 1, isperformed. Accordingly, in the battery electrode plate 19 obtained inthe embodiment, the core substrate exposed section 13 can be folded andthen compressed to produce the current collector 19 b, and by so doing,the mechanical strength and the density of the current collector 19 b isincreased, and moreover, the current collecting efficiency is alsoimproved.

[0045] Furthermore, in the battery electrode plate 19, the variation inthe impregnation density of the active material impregnated section 19 ais suppressed to no more than 1.5%. This is because the active material3 is. impregnated into the smooth core substrate 1 prior to pressworking. In contrast, in a battery electrode plate 7 obtained byconventional method, a core substrate 1 which has been press worked andincludes surface irregularities is impregnated with the active material3, and so it is impossible to ensure a uniform degree of impregnationacross the entire substrate, and the active material impregnated section7 a displays a variation in impregnation density of at least 3.5%.

[0046]FIG. 4 shows a nickel-metal hydride battery in which an electrodegroup 51, including battery electrode plates 19 p, 19 q of a positiveelectrode and a negative electrode produced by the above-describedmethod spirally wound with a separator 55 interposed therebetween, ishoused inside a cylindrical battery case 52. In this cylindricalbattery, a positive electrode terminal 56 of a sealing plate 57, and thepositive electrode plate 19 p are electrically connected via a lead, andthe battery case 52 which functions as a negative electrode, and thenegative electrode plate 19 q are electrically connected via a lead. Theinside of the battery case 52 is filled with an electrolyte.

[0047]FIG. 5A through FIG. 5G are perspective views showing the sequenceof production steps in a method for manufacturing a battery electrodeplate according to a second embodiment of the present invention. Theaforementioned first embodiment described a method for manufacturing abattery electrode plate 19 for forming a spirally wound electrode groupfor use in a cylindrical battery, whereas this second embodiment relatesto a method of manufacturing battery electrode plates for forming alaminated electrode group for use in a prismatic battery. In FIG. 5Athrough FIG. 5G, those components which are identical with, orequivalent to those shown in FIG. 1A through FIG. 1F are labeled withthe same reference numerals.

[0048] First, an entire core substrate 1 formed from a rectangular orstrip shaped piece of foamed metal of a predetermined size, as shown inFIG. 5A, is impregnated with an active material 3 as shown in FIG. 5B.In this case, the active material 3 is impregnated into a totally flatcore substrate 1 prior to press working, and so is impregnated with auniform density throughout the entire core substrate 1, and moreoverbecause the surface of the core substrate 1 is not irregular, namelythere are no elevation differences, the active material 3 is retainedwithin the substrate without flowing, and consequently dries with theuniform impregnation density maintained.

[0049] Next, as shown in FIG. 5C, the entire surface of the coresubstrate 1 uniformly impregnated with the active material 3, with theexception of those sections which form core substrate exposed sectionsin subsequent steps, is subjected to press working, and the thickness ofthe substrate is compressed to approximately half, and the sectionswhich form core substrate exposed sections in subsequent steps are leftas two parallel rail shaped protrusions 20, 20. In this pressing step, astripe roller press device (not shown in the drawings) of the same basicconstruction as the stripe roller press device 9 shown in FIG. 2A isused, and includes a working press roller with annular slots provided atpositions corresponding to the protrusions 20, 20 shown in FIG. 5C.

[0050] Subsequently, in an active material removal step, the activematerial 3 impregnated within the two protrusions 20, 20 is removed toform two core substrate exposed sections 21, 21. In this active materialremoval step, an active material removal device (not shown in thedrawings) is used which has a construction almost identical with that ofthe active material removal device 14 including an ultrasonic vibrationdevice 17 shown in FIG. 3A and FIG. 3B, and the processing performed isidentical with that described for the first embodiment.

[0051] The core substrate exposed sections 21, 21 are then lightlycompressed using a press roller (not shown in the drawings), in asimilar manner to the first embodiment, to yield a state in which thecore substrate exposed sections 21, 21 are level with the other regionscontaining active material 3. Subsequently, as shown in FIG. 5D, theaforementioned core substrate exposed sections 21, 21 are furthercompressed using the press roller so that the upper surfaces thereof areat a lower level than the regions containing active material 3. Next, astrip shaped lead, namely a lead hoop 22, is seam welded to each of thecore substrate exposed sections 21, 21. Finally, by cutting or punchingalong each of the cutting lines shown by alternate long and short dashlines in FIG. 5F, a plurality of battery electrode plates 23 shown inFIG. 5G are obtained. Each of these battery electrode plates 23 are ofthe same form, and include an active material impregnated section 23 a,a current collector 23 b from which the active material 3 has beenremoved, and a lead plate 23 c which is fixed to the current collector23 b.

[0052] This method for manufacturing a battery electrode plate 23includes essentially the same steps as the first embodiment, and as suchis capable of achieving similar effects to those described above for thefirst embodiment, and so high quality battery electrode plates 23 foruse in a prismatic battery are produced with high productivity.Moreover, instead of the step for welding the lead hoop 22, the activematerial impregnated core substrate 1 without a welded lead hoop 22could also be divided in two by cutting along the cutting line showndown the center of FIG. 5F, the core substrate exposed section 21 thenfolded over and compressed to form a current collector, and thesubstrate then divided into individual battery electrode plates. Theaforementioned process increases the mechanical strength and the densityof the current collector, and also improves the current collectionefficiency, and consequently enables the formation of a stable leadfragment with the same high quality as the lead plate 23 c provided bycutting the lead hoop 22.

[0053]FIG. 6 shows a nickel-metal hydride battery in which an electrodegroup 53, including battery electrode plates 23 p, 23 q of a positiveelectrode and a negative electrode produced by the above-describedmethod laminated alternately with a separator 58 interposedtherebetween, is housed inside a prismatic battery case 54. In thisprismatic battery, a positive electrode terminal 60 of a sealing plate59, and the positive electrode plate 23 p are electrically connected viaa lead, and the battery case 54 which functions as a negative electrode,and the negative electrode plate 23 q are electrically connected via alead. The inside of the battery case 54 is filled with an electrolyte.

Industrial Applicability

[0054] According to the present invention, a battery electrode plate isobtained in which there is no variation in the impregnation density ofthe active material, the boundary line between the active materialimpregnated section and the current collector is a true straight line,the residual ratio of the active material in the current collector islow, and the entire current collector has a predetermined width.Consequently, the present invention is very useful for producing, withgood efficiency, a battery with a high degree of high rate dischargecharacteristics.

1. A prismatic battery comprising: an electrode group formed frombattery electrode plates of a positive electrode and a negativeelectrode laminated alternately with a separator interposedtherebetween; and a prismatic battery case for housing said electrodegroup; at least one of the battery electrode plates being manufacturedby a method comprising: an active material impregnation step forimpregnating an entire porous core substrate shaped like a thin platewith an active material; a pressing step for performing press working onsaid active material impregnated core substrate to form a plurality ofrail shaped protrusions; an active material removal step for removingthe active material to form core substrate exposed sections by applyingultrasonic vibrations to said rail shaped protrusions; a core substrateexposed section compression step for compressing said core substrateexposed sections; a lead welding step for seam welding a lead hoop tosaid core substrate exposed sections; and a cutting step for cuttingpredetermined sections including said lead hoop to form a batteryelectrode plate.
 2. A prismatic battery according to claim 1, in whichthe positive and the negative electrode plates are manufactured by saidmethod.